Conveyor control systems have in the past included chains running along the guide rails to which each trolley is connected. Speed is constant as is spacing between the vehicles. The problem with this type of assembly is that if the chain breaks down or one of the vehicles breaks down, the entire system is at a halt. Therefore, conveyor control systems are using vehicles which have a motor thereon to turn the wheels which receives power from power rails running along the guide rails. Each vehicle is self propelled so that if one of the vehicles breaks down, the vehicle can be removed without a total shut down of the conveyor system.
One such type of assembly includes self propelled vehicles having a drive motor supplied with power via current rail. The vehicles have contact elements extending out from their structures to open the circuit to slow or stop the vehicle when contact is made with another vehicle. A problem with this type of assembly is that the vehicles move at one speed and a collision is necessary before the motor is turned off. Such a system is disclosed in the U.S. Pat. No. 3,823,673 granted July 16, 1974 in the name Erich Wesener which discloses a conveyor control system using vehicles containing a motor which are powered by current rails wherein a circuit is opened when contact occurs between two vehicles.